WEBVTT 00:00:07.449 --> 00:00:10.109 Howdy Star Gazers and welcome to this episode 00:00:10.109 --> 00:00:13.429 of Star Trails. Drew here and I'll be your guide 00:00:13.429 --> 00:00:16.089 to the night sky for the week starting July the 00:00:16.089 --> 00:00:19.929 6th through the 12th. This week we answer some 00:00:19.929 --> 00:00:23.489 listener mail and explore the mystery of mass. 00:00:23.820 --> 00:00:27.899 A big full moon looms low on the horizon, and 00:00:27.899 --> 00:00:30.899 we take a detour into the icy reaches of our 00:00:30.899 --> 00:00:34.219 solar system, where relics of the early universe 00:00:34.219 --> 00:00:37.240 hide away in the darkness. Whether you're tuning 00:00:37.240 --> 00:00:40.119 in from the backyard, the balcony, or just your 00:00:40.119 --> 00:00:43.280 imagination, I'm glad you're here. So find a 00:00:43.280 --> 00:00:46.320 cozy spot, let your eyes adjust, and let's see 00:00:46.320 --> 00:00:50.649 what the sky holds for us this week. Before we 00:00:50.649 --> 00:00:53.070 get into the night sky this week, I'd like to 00:00:53.070 --> 00:00:55.570 kick off this episode with a listener question, 00:00:55.789 --> 00:00:58.869 and this one really hits the sweet spot. Simple 00:00:58.869 --> 00:01:02.049 on the surface, but it opens the door to something 00:01:02.049 --> 00:01:06.409 surprisingly deep. Last week, Dale from Omaha 00:01:06.409 --> 00:01:10.150 wrote, Can you explain mass? I don't understand 00:01:10.150 --> 00:01:14.140 how mass is calculated or what that means. I've 00:01:14.140 --> 00:01:17.280 heard astrophysicists say two planets are the 00:01:17.280 --> 00:01:21.000 same size but have different masses. A simple 00:01:21.000 --> 00:01:24.900 explanation would be greatly appreciated. Dale, 00:01:24.939 --> 00:01:27.519 first off, thanks for writing in with this question, 00:01:27.659 --> 00:01:30.439 and I know you asked for a simple explanation, 00:01:30.500 --> 00:01:34.019 and I intend to provide one, but mass, although 00:01:34.019 --> 00:01:37.000 a reasonably straightforward concept in and of 00:01:37.000 --> 00:01:40.290 itself, is connected to some of the real mysteries 00:01:40.290 --> 00:01:43.609 of astrophysics and the workings of the universe. 00:01:44.549 --> 00:01:46.750 I'll get into a few of those in a moment, but 00:01:46.750 --> 00:01:49.329 let's first figure out what's going on at the 00:01:49.329 --> 00:01:53.829 most basic level. Mass is essentially how much 00:01:53.829 --> 00:01:56.989 stuff is packed into something. It's not about 00:01:56.989 --> 00:01:59.890 how big something looks, it's about how much 00:01:59.890 --> 00:02:03.629 material is actually in there. Think about two 00:02:03.629 --> 00:02:07.290 identical suitcases. One is filled with clothes, 00:02:07.519 --> 00:02:10.639 The other is packed with bricks. They take up 00:02:10.639 --> 00:02:13.199 the same space, but the one with bricks is a 00:02:13.199 --> 00:02:16.580 lot heavier. That's because it has more mass. 00:02:17.439 --> 00:02:20.759 Astronomers talk about mass all the time. Just 00:02:20.759 --> 00:02:23.780 like your question, two planets can be the same 00:02:23.780 --> 00:02:27.879 size, but one can have more mass. That means 00:02:27.879 --> 00:02:31.479 one is denser. Maybe it has a larger metal core 00:02:31.479 --> 00:02:36.360 or more rock and less gas. Same outside dimensions, 00:02:36.639 --> 00:02:39.919 but more weight on the inside. Let's consider 00:02:39.919 --> 00:02:44.360 Earth's planetary sister, Venus. Both Earth and 00:02:44.360 --> 00:02:47.719 Venus are roughly the same size, but Earth has 00:02:47.719 --> 00:02:51.240 more mass thanks to its larger metallic core. 00:02:52.120 --> 00:02:54.780 Let's take another example. Because it's summer, 00:02:55.000 --> 00:02:57.879 let's consider a beach ball compared to a bowling 00:02:57.879 --> 00:03:02.060 ball, maybe a good 16 -pounder. The beach ball 00:03:02.060 --> 00:03:05.159 is very light, but much larger than the bowling 00:03:05.159 --> 00:03:09.159 ball. The beach ball contains mostly air, while 00:03:09.159 --> 00:03:12.020 the bowling ball is filled with, well, whatever 00:03:12.020 --> 00:03:15.719 bowling balls are made of, dense resin or plastics, 00:03:15.719 --> 00:03:19.740 I assume. It's that density that matters, rather 00:03:19.740 --> 00:03:23.319 than the size. And density is what determines 00:03:23.319 --> 00:03:26.560 mass. Now, here's where things start to become 00:03:26.560 --> 00:03:30.259 fascinating. Let's shrink ourselves down to the 00:03:30.259 --> 00:03:33.479 molecular level. If you were to stand next to 00:03:33.479 --> 00:03:36.479 a beach ball and a bowling ball at this tiny 00:03:36.479 --> 00:03:39.699 size, you'd feel a gravitational pull towards 00:03:39.699 --> 00:03:44.439 the bowling ball. Mass is directly tied to gravity. 00:03:45.020 --> 00:03:48.080 The more mass something has, the stronger its 00:03:48.080 --> 00:03:51.719 gravitational pull. Earth pulls harder than the 00:03:51.719 --> 00:03:55.219 moon because it has more mass. The Sun keeps 00:03:55.219 --> 00:03:58.639 the planets in orbit because it's massive, not 00:03:58.639 --> 00:04:01.759 just in size, as the term is often used, but 00:04:01.759 --> 00:04:05.060 in actual weight. In astronomy, we can't weigh 00:04:05.060 --> 00:04:08.960 things directly, so we figure out mass by watching 00:04:08.960 --> 00:04:12.879 how objects move. For example, how fast a moon 00:04:12.879 --> 00:04:16.720 orbits a planet. That motion tells us how much 00:04:16.720 --> 00:04:20.339 gravity there is, and gravity tells us the mass. 00:04:21.180 --> 00:04:24.689 Now let's get weird. Mass accounts for some of 00:04:24.689 --> 00:04:27.490 the most fascinating phenomena in the universe, 00:04:27.910 --> 00:04:30.970 including one of the most extreme, black holes. 00:04:31.949 --> 00:04:35.269 These are the ultimate examples of mass and gravity 00:04:35.269 --> 00:04:39.709 gone wild. A black hole forms when a giant star 00:04:39.709 --> 00:04:43.490 collapses and all that mass gets squeezed into 00:04:43.490 --> 00:04:47.509 an incredibly tiny space. Imagine taking something 00:04:47.509 --> 00:04:50.790 more massive than the sun and cramming it into 00:04:50.790 --> 00:04:53.949 something the size of a city or smaller. The 00:04:53.949 --> 00:04:58.449 result is unbelievably dense. Now remember, gravity 00:04:58.449 --> 00:05:02.050 depends on mass, and our distance to an object 00:05:02.050 --> 00:05:06.189 alters how much gravity we experience. Because 00:05:06.189 --> 00:05:09.350 black holes are so compact, you can get extremely 00:05:09.350 --> 00:05:12.050 close to them. But if you get too close, you 00:05:12.050 --> 00:05:15.490 get sucked in, and there's no turning back. The 00:05:15.490 --> 00:05:18.449 gravity near them is so strong that even light 00:05:18.449 --> 00:05:22.850 can't escape. That's why they're black. If, purely 00:05:22.850 --> 00:05:26.029 as a thought experiment, our sun turned into 00:05:26.029 --> 00:05:28.910 a black hole, Earth would keep orbiting just 00:05:28.910 --> 00:05:32.829 like it does now, same mass, same distance. But 00:05:32.829 --> 00:05:35.490 if you flew close to that black hole, you'd cross 00:05:35.490 --> 00:05:38.610 a point of no return, where gravity takes over 00:05:38.610 --> 00:05:41.740 and there's no way back. We've understood the 00:05:41.740 --> 00:05:44.819 relationship between mass and gravity for a while. 00:05:45.000 --> 00:05:48.600 This was Isaac Newton's great breakthrough, later 00:05:48.600 --> 00:05:51.920 expanded by Einstein and his theories of relativity 00:05:51.920 --> 00:05:56.120 and space -time. Einstein also taught us that 00:05:56.120 --> 00:05:59.740 energy and mass are basically interchangeable. 00:06:00.079 --> 00:06:03.540 That, of course, is his famous equation E equals 00:06:03.540 --> 00:06:07.120 mc squared. But interestingly, we don't really 00:06:07.120 --> 00:06:11.220 know why mass affects gravity. This is one of 00:06:11.220 --> 00:06:13.800 the real unsolved mysteries of the universe. 00:06:13.980 --> 00:06:17.160 We just know that it does and that we can directly 00:06:17.160 --> 00:06:20.399 observe its effect. There are some interesting 00:06:20.399 --> 00:06:24.060 theories, gravitons for instance, particles that 00:06:24.060 --> 00:06:27.600 somehow influence gravity. There are string theories 00:06:27.600 --> 00:06:31.459 and theories based on that energy to mass relationship, 00:06:31.459 --> 00:06:35.639 but so far we just don't really know. But we 00:06:35.639 --> 00:06:39.439 do know what mass is and we know it shapes gravity. 00:06:39.610 --> 00:06:43.670 motion, orbits, and the entire cosmic dance. 00:06:44.550 --> 00:06:46.550 I know we went down a bit of a rabbit hole there, 00:06:46.569 --> 00:06:49.769 but hopefully we answered the question. If anyone 00:06:49.769 --> 00:06:52.110 out there listening has a question or a topic 00:06:52.110 --> 00:06:55.290 they'd like for me to cover, just visit our website, 00:06:55.649 --> 00:06:59.930 StarTrails .Show, and hit the contact link. Dale, 00:07:00.290 --> 00:07:10.170 thanks so much for writing in. The night sky 00:07:10.170 --> 00:07:13.490 is fairly quiet this week, and it will be dominated 00:07:13.490 --> 00:07:17.089 by the upcoming full moon. On Thursday, we're 00:07:17.089 --> 00:07:20.810 treated to the full buck moon rising in the evening 00:07:20.810 --> 00:07:24.470 sky. The buck moon is the traditional name given 00:07:24.470 --> 00:07:27.910 to July's full moon. It comes from, you guessed 00:07:27.910 --> 00:07:31.350 it, Native American traditions, named after the 00:07:31.350 --> 00:07:34.069 time of year when male deer began to grow their 00:07:34.069 --> 00:07:38.290 new antlers. It's a moment that marks high summer, 00:07:38.430 --> 00:07:40.930 and this year's buck moon has a little extra 00:07:40.930 --> 00:07:43.629 drama. Because it's rising low on the horizon, 00:07:44.069 --> 00:07:46.769 we'll experience what's known as the moon illusion. 00:07:47.389 --> 00:07:50.069 That trick of the eye where the moon looks huge 00:07:50.069 --> 00:07:53.089 when it's near the horizon, especially just after 00:07:53.089 --> 00:07:57.029 it rises. Our brains compare it to nearby objects 00:07:57.029 --> 00:08:00.449 like trees or rooftops, and we perceive it as 00:08:00.449 --> 00:08:03.819 being much larger. It's a gorgeous effect, and 00:08:03.819 --> 00:08:06.459 one of the best full moons of the year to photograph 00:08:06.459 --> 00:08:10.220 if you have clear skies in your area. Now onto 00:08:10.220 --> 00:08:13.839 the planets. Mercury is hanging out low in the 00:08:13.839 --> 00:08:17.519 west -northwest just after sunset around magnitude 00:08:17.519 --> 00:08:21.480 .3. Best seen early this week if you have a clear 00:08:21.480 --> 00:08:25.000 view of the horizon. Mars is hanging out in the 00:08:25.000 --> 00:08:28.480 west, still reddish but fading into the twilight. 00:08:29.180 --> 00:08:32.740 Saturn and Neptune are up in Pisces, rising late 00:08:32.740 --> 00:08:36.039 and sticking around into the night. Over in the 00:08:36.039 --> 00:08:39.539 predawn sky, Venus is bright and unmistakable 00:08:39.539 --> 00:08:42.840 in the east. Later in the week, it's joined by 00:08:42.840 --> 00:08:46.779 a faint Uranus hiding in Taurus. As always, you'll 00:08:46.779 --> 00:08:49.980 need a scope or good binoculars to spot Uranus 00:08:49.980 --> 00:08:54.019 and Neptune. It's still early, but meteor season 00:08:54.019 --> 00:08:57.929 is just around the corner. The Alpha Capra cornids 00:08:57.929 --> 00:09:01.769 begin trickling in this week. Slow moving fireballs, 00:09:02.090 --> 00:09:05.809 best later in July. And if you're a Perseid fan, 00:09:06.110 --> 00:09:08.269 we're only about a week away from the start of 00:09:08.269 --> 00:09:17.669 that shower's long lead up. Have you ever considered 00:09:17.669 --> 00:09:21.470 how far our solar system extends from the sun? 00:09:21.759 --> 00:09:24.799 In this episode, we're taking a little detour 00:09:24.799 --> 00:09:28.299 beyond the outer planets into the frozen frontiers 00:09:28.299 --> 00:09:31.559 of our solar system. We'll explore two of the 00:09:31.559 --> 00:09:34.519 most mysterious regions we've never actually 00:09:34.519 --> 00:09:38.240 seen with our own eyes, the Kuiper Belt and the 00:09:38.240 --> 00:09:42.740 Oort Cloud. These are the deep freeze zones of 00:09:42.740 --> 00:09:47.000 the cosmos, full of ancient icy leftovers, silent 00:09:47.000 --> 00:09:50.539 travelers, and even the occasional supersized 00:09:50.539 --> 00:09:54.090 comet. Let's start with the one closer to us. 00:09:54.590 --> 00:09:57.190 The Kuiper Belt, named after the Dutch -American 00:09:57.190 --> 00:10:01.309 astronomer Gerard Kuiper, is a ring of icy bodies 00:10:01.309 --> 00:10:04.809 orbiting the sun beyond Neptune, starting around 00:10:04.809 --> 00:10:08.889 30 astronomical units out. At that distance, 00:10:09.330 --> 00:10:11.809 sunlight is a pale glow, and the temperature 00:10:11.809 --> 00:10:16.070 is hundreds of degrees below zero. The Kuiper 00:10:16.070 --> 00:10:19.519 Belt is the solar system's icy junkyard. It's 00:10:19.519 --> 00:10:21.919 full of leftover material from when the planets 00:10:21.919 --> 00:10:26.639 formed about 4 .6 billion years ago. We're talking 00:10:26.639 --> 00:10:31.080 rocks, frozen gases, chunks of water ice, and 00:10:31.080 --> 00:10:33.919 other elements that never made it into planets. 00:10:34.940 --> 00:10:38.299 It's also home to some famous objects. Pluto, 00:10:38.700 --> 00:10:42.740 of course, demoted from planet status in 2006, 00:10:43.299 --> 00:10:47.110 is proudly orbiting in the Kuiper Belt. Eris 00:10:47.110 --> 00:10:50.190 is slightly smaller than Pluto, but helped force 00:10:50.190 --> 00:10:53.389 that whole redefinition of what a planet is. 00:10:54.149 --> 00:10:57.669 Then there's Haumea, shaped like a football and 00:10:57.669 --> 00:11:00.629 spinning so fast it completes a rotation every 00:11:00.629 --> 00:11:05.049 four hours. And Machi Machi, another dwarf planet 00:11:05.049 --> 00:11:09.279 named after a Polynesian creator god. These icy 00:11:09.279 --> 00:11:14.059 worlds are known as Kuiper Belt Objects, or KBOs. 00:11:14.259 --> 00:11:17.440 Many of them have moons, some have strange orbits, 00:11:17.620 --> 00:11:20.240 and there are probably hundreds of thousands 00:11:20.240 --> 00:11:24.779 more we haven't seen yet. NASA's New Horizons 00:11:24.779 --> 00:11:29.220 mission flew past Pluto in 2015, revealing its 00:11:29.220 --> 00:11:32.620 icy mountains, nitrogen glaciers, and unexpected 00:11:32.620 --> 00:11:36.500 complexity. And then it kept going. sending back 00:11:36.500 --> 00:11:41.539 images of another KBO, Arakoth, a reddish snowman 00:11:41.539 --> 00:11:45.940 -shaped object about 21 miles long. That flyby 00:11:45.940 --> 00:11:49.940 in 2019 gave us our very first close -up of a 00:11:49.940 --> 00:11:54.019 true Kuiper Belt object. Now let's take a quick 00:11:54.019 --> 00:11:58.100 detour about comets, snowballs in space with 00:11:58.100 --> 00:12:02.480 glowing tails. Short period comets swing by the 00:12:02.480 --> 00:12:05.340 Sun every few decades and often come from the 00:12:05.340 --> 00:12:09.299 Kuiper Belt. Think of Comet Halley or Comet Temple 00:12:09.299 --> 00:12:13.220 Tuttle. These objects orbit in more or less the 00:12:13.220 --> 00:12:16.059 same plane as the planets, and their orbits are 00:12:16.059 --> 00:12:19.000 usually predictable. But then there are the weird 00:12:19.000 --> 00:12:22.820 ones, the comets with giant lopsided orbits that 00:12:22.820 --> 00:12:26.120 take millions of years to return. That brings 00:12:26.120 --> 00:12:30.210 us to our next destination. Far beyond the Kuiper 00:12:30.210 --> 00:12:34.669 belt, somewhere between 2 ,000 and 100 ,000 astronomical 00:12:34.669 --> 00:12:38.309 units from the Sun is a theoretical shell of 00:12:38.309 --> 00:12:42.490 icy bodies called the Oort cloud. Unlike the 00:12:42.490 --> 00:12:45.690 flat disc -shaped Kuiper belt, the Oort cloud 00:12:45.690 --> 00:12:50.269 is spherical. Imagine a vast snow globe surrounding 00:12:50.269 --> 00:12:53.649 our entire solar system, and inside that globe 00:12:53.649 --> 00:12:57.480 are potentially trillions of icy fragments. comets, 00:12:57.840 --> 00:13:01.120 planetesimals, ancient debris, left over from 00:13:01.120 --> 00:13:05.200 the very formation of the Sun. We've never directly 00:13:05.200 --> 00:13:08.899 seen the Oort cloud, it's just too far. But we 00:13:08.899 --> 00:13:11.159 know it's there because of those long period 00:13:11.159 --> 00:13:14.360 comets that suddenly appear from deep space on 00:13:14.360 --> 00:13:18.279 incredibly eccentric orbits. Comets like Hale 00:13:18.279 --> 00:13:22.799 -Bopp, which passed by in 1997 and won't return 00:13:22.799 --> 00:13:27.210 for another 2500 years. Another such visitor 00:13:27.210 --> 00:13:32.909 was comet C2012S1, which was hyped in 2013, but 00:13:32.909 --> 00:13:36.250 broke apart near the Sun. And more recently, 00:13:36.549 --> 00:13:39.029 there's a mega comet, and we mentioned this one 00:13:39.029 --> 00:13:44.450 last week. In 2021, astronomers Pedro Bernardinelli 00:13:44.450 --> 00:13:47.769 and Gary Bernstein spotted something strange 00:13:47.769 --> 00:13:51.440 in data from the Dark Energy Survey. A fuzzy, 00:13:51.580 --> 00:13:55.299 slow -moving object as wide as 85 miles across. 00:13:55.980 --> 00:14:00.179 That's bigger than some small moons. Named comet 00:14:00.179 --> 00:14:03.039 Bernardinelli -Bernstein, it's considered the 00:14:03.039 --> 00:14:06.840 largest comet nucleus ever discovered. It's not 00:14:06.840 --> 00:14:09.799 coming anywhere near Earth. At its closest approach 00:14:09.799 --> 00:14:14.600 in 2031, it'll still be out past Saturn. Even 00:14:14.600 --> 00:14:16.600 though we won't be able to see it with the naked 00:14:16.600 --> 00:14:20.019 eye, this comet is giving scientists a rare opportunity 00:14:20.019 --> 00:14:23.600 to study a pristine, early solar system object, 00:14:24.240 --> 00:14:27.960 probably untouched since the sun was born. That's 00:14:27.960 --> 00:14:30.259 like getting a piece of solar system history 00:14:30.259 --> 00:14:34.639 frozen in deep space for billions of years. These 00:14:34.639 --> 00:14:37.720 frozen regions are like the archives of the solar 00:14:37.720 --> 00:14:41.299 system. The Kuiper Belt and the Oort Cloud preserve 00:14:41.299 --> 00:14:43.980 the raw materials from the early days of planet 00:14:43.980 --> 00:14:47.639 building, before Earth had oceans or life or 00:14:47.639 --> 00:14:51.580 even before Jupiter finished forming. Some scientists 00:14:51.580 --> 00:14:54.320 believe that comets from these outer zones delivered 00:14:54.320 --> 00:14:57.720 water and organic molecules to the early Earth. 00:14:58.399 --> 00:15:01.480 Others are looking into whether Oort Cloud comets 00:15:01.480 --> 00:15:04.980 could help explain the odd tilt of Uranus or 00:15:04.980 --> 00:15:08.620 even the idea of a hypothetical Planet Nine lurking 00:15:08.620 --> 00:15:11.860 in the darkness. And that's our journey to the 00:15:11.860 --> 00:15:15.259 far edge of the Sun's influence. From Pluto's 00:15:15.259 --> 00:15:18.080 neighborhood to the Oort Cloud's distant reaches, 00:15:18.519 --> 00:15:21.120 the outer solar system is more than just empty 00:15:21.120 --> 00:15:30.629 space. It's a museum of frozen time. If the stars 00:15:30.629 --> 00:15:32.950 spoke to you this week or if a question's been 00:15:32.950 --> 00:15:35.690 on your mind, I'd love to hear it. Visit our 00:15:35.690 --> 00:15:39.350 website, StarTrails .Show, where you can contact 00:15:39.350 --> 00:15:43.129 me and explore past episodes. Be sure to follow 00:15:43.129 --> 00:15:46.509 us on Blue Sky and YouTube. Links are in the 00:15:46.509 --> 00:15:49.789 show notes. Until we meet again beneath the stars, 00:15:50.409 --> 00:15:51.429 clear skies, everyone.